This invention relates to sofa bed mechanisms of the type wherein a bed frame comprising side and end rails is mounted within a sofa frame for movement between an unfolded substantially planar bed position and a folded sofa position in which the bed frame is stored within the sofa frame. Among the principal objectives in mechanisms of this type is to provide firm, comfortable support for users in the bed position. Unfortunately, in the prior art mechanisms, the goals of "firmness" and "comfort" have rarely been achieved concurrently.
For example, U.S. Pat. No. 4,236,260, assigned to the assignee of the present invention, describes a sofa bed mechanism wherein a polypropylene fabric deck is stretched across the bed frame and secured to the side rails. This type of mechanism has been generally satisfactory both from the standpoint of firmness and comfort. However, there is a tendency in some situations for the polyproylene deck to experience localized sagging under the weight of an occupant, especially under the occupant's shoulders where weight is concentrated. Sagging results from the side rails of the bed frame being drawn inwardly by the deck under load, and detracts from the firmness and comfort of the mechanism.
Even less satisfactory from a comfort standpoint have been conventional mechanisms employing rigid cross tubes which extend between the side rails of the bed frame. These mechanisms have generally provided firm support, since the rigid cross tubes keep the side rails spaced apart. However, the cross rails have been extremely uncomfortable to bed users, especially in the shoulder area, since they protrude into users' backs.
Another problem frequently encountered in sofa bed mechanisms is in the legs used to support the unfolded bed frame on the floor. These legs must be strong enough to support the bed frame, yet they must not be so bulky as to significantly add to the dimensions of the folded unit when the bed frame is stored. Again, these dual objectives have rarely been met in a single prior art device.
It is an object of the present invention, therefore, to provide an improved sofa bed mechanism with improved back support to meet the aforementioned requirements of firmness and comfort.
It is another object of this invention to provide a sofa bed mechanism with improved support legs having improved strength characteristics while minimizing the amount of space taken up in the folded position.